Media gateway controller (MGC) and media gateway (MG) are two key components in a packet-based network with an architecture where services are separated from bearers. The MGC is mainly responsible for service control, while the MG is mainly responsible for media bearing. The gateway-separation architecture formed by the MGC and the MG realizes the separation of a service control plane and a media bearing plane, so that network resources can be better shared, device upgrading and service extension can be simplified, and the development and maintenance costs can be reduced.
The MG and the MGC communicate with each other by using a media gateway control protocol. The currently prevalent protocols include the H.248/Gateway Control Protocol (MeGaCo) and MGCP. The MGCP is developed and amended by the Internet Engineering Task Force (IETF). The H.248/MeGaCo protocol is developed based on the MGCP. H.248/MeGaCo version 1 was set down by the IETF and the International Telecommunications Union (ITU) together in November, 2000 and was amended in June, 2003. H.248 version 2 was set down by the ITU in May, 2002 and was amended in March, 2004. H.248 version 3 was set down by the ITU in September, 2005.
Currently, a connection model defined by the H.248/MeGaCo protocol includes termination and context. A termination is a logic entity in the MG (the MG itself may also be represented as a termination called a Root termination), which is used for sending and receiving one or more media. Terminations are further divided into Physical terminations and Ephemeral terminations. Physical terminations represent some semi-permanent physical entities such as Time Division Multiplex (TDM) timeslots or analog lines. Ephemeral terminations represent some public resources that are applied for temporarily and released after being used, for example, streams based on the Real-time Transport Protocol (RTP). The characteristics of a termination are represented with Property, Signal, Event, Statistic, etc (which are referred to as parameter descriptors), and a package is introduced to combine various characteristic parameters of the termination. In addition, a context represents an association between terminations. One context may include a plurality of terminations, and a topology is used for describing interrelations between the terminations. A termination that is not associated with other terminations yet is contained in a special context called a Null context. The context is created when the first termination is added, and is released when the last termination is removed.
Based on the abstract connection model, an interaction between a service and a bearer is actually an operation on terminations and context, which is realized by the Request and Reply of the command between the MGC and the MG. The types of the command include Add, Modify, Subtract, Move, AuditValue, AuditCapabilities, Notify, ServiceChange, etc.
A signal is adopted by the MGC to instruct the MG to perform a resource operation, for example, playing tone. The signal is executed in termination or stream level, and when the signal is executed on a termination, it indicates that the signal is applicable to all streams on the termination. A series of operations that need to be performed sequentially may be represented in a form of a signal list, and intervals may exist among operations. The MGC includes a signal and/or signal list in a signal descriptor and delivers the signal descriptor to the MG. The signals and/or signal lists in the signal descriptors that are delivered at the same time are executed synchronously.
The control over signal delivery bandwidth is exercised according to certain settings in advance, for example, the speed for transferring a configured medium is 100 Kbps by default. Subsequently, the medium is transferred at this speed, but a possibility of adjusting a signal delivery bandwidth exists in actual applications, for example, it is expected that the medium in the above instance is transferred at a speed of 500 Kbps or 50 Kbps, so as to preview the medium at a higher or lower speed or at a high or low quality. At present, the MGCP cannot support the adjustment of a signal delivery bandwidth.